Paving machines are used for depositing, spreading, compacting, and smoothing paving material on a roadbed in such a manner that a uniform and drivable surface is produced. In the case of an asphalt paving machine, the paving material is typically an aggregate filled bituminous mixture that is deposited on a roadbed while hot. Once the mixture cools after being suitably compacted and smoothed, a hardened pavement surface results.
Paving machines use screed assemblies to smooth and compact the paving material. The screed assembly is typically drawn behind the paving machine and is adjustable to establish the thickness of the deposited layer of paving material.
A screed assembly typically includes a base portion and may include one or more extension portions, each of these portions having steel screed plates mounted to the screed portions in such a manner that the plates both smooth and compress the deposited paving material, leaving behind a mat of the desired thickness. The screed plates are typically heated to prevent the bituminous material from clinging to the steel plates. In modem screed assemblies, the screed plate heaters are commonly implemented in the form of resistive electrical heaters that can be optimally positioned on or near the screed plates. Screed plates may also be heated by gas or other combustible fuel heaters.
It is important to maintain a proper screed plate temperature. If the screed plates are either too hot or too cold, a poor finish will be obtained in the resulting pavement mat. In a simple screed having only base screed portions, each of the base screed portions typically includes both a heater and a temperature sensor. In such a system, each of the base screed plates may be individually temperature controlled according to feedback received from the associated temperature sensor.
However, many screed assemblies make provision for attaching extension screeds to the ends of the base screed portions. These extension screed portions must be mechanically connected to the base screed portions, and must also be connected to provide controlled power to the heating elements. It is known to merely connect the heating elements of the extension screed portions in parallel with the heating elements of the base screed. In such a configuration, the extension screed heaters are controlled in response to temperature sensors located on the base screed portion. Consequently, the extension screed portions may be either too hot or too cold to produce a desired mat finish.
The present invention is directed to overcoming one or more of the problem set forth above.